As a catalyst for producing a polyalkylene oxide by ring-opening polymerization of an alkylene oxide, for example, an active hydrogen compound and a compound represented by Zn3[Fe(CN)6]2.H2O.dioxane are known (e.g. Patent Document 1). Further, it is known to use a zinc hexacyanocobaltate complex as the catalyst (e.g. Patent Document 2). It is further known to use, as the catalyst, a product obtained by adding a solution of diethylzinc in hexane to a dispersion obtained by adding 1,4-butanediol and a non-ionic surfactant to a slurry of fumed silica in hexane (e.g. Patent Document 3). However, each of the catalysts disclosed in these documents, contains a special metal component, and if such a metal component remains in the formed polyalkylene oxide, it adversely affects the reaction during the production of a polyurethane or the physical properties of the polyurethane. Accordingly, in the production of a polyalkylene oxide, a special method or cumbersome steps are required to sufficiently remove such a metal component.
On the other hand, as a catalyst containing no metal, patent Document 4 discloses a catalyst which is combination of an alkane polyol being an active hydrogen compound and an ether adduct of boron trifluoride. However, it is known that a peculiar impurity in the polymer obtainable by this catalyst system adversely affects the physical properties of a polyurethane, and cumbersome steps are required to sufficiently remove such an impurity. Further, Patent Document 5 discloses to obtain a polymer of an alkylene oxide by using an alcohol and an amino phenol as catalysts, and Patent Document 6 discloses to polymerize propylene oxide by using sorbitol and tetramethyl ammonium hydroxide. However, in each of the cases where the catalysts disclosed in these documents are used, the polymerization activity is not sufficient, and there is a problem such that an amine type odor remains.
Further, it is known that a phosphazenium salt of an active hydrogen compound represented by the following formula:
[in the above formula, n is an integer of from 1 to 8 and represents the number of phosphazenium cations, Zn− is an n-valent active hydrogen compound anion in the form obtained by removing n protons from an active hydrogen compound having at most 8 active hydrogen atoms on oxygen atoms or nitrogen atoms, and each of a, b, c and d is a positive integer of at most 3, or 0, provided that all of them are not simultaneously 0, and R's are the same or different C1-10 hydrocarbon groups, provided that two R's on the same nitrogen atom may be bonded to each other to form a ring structure] is obtained by reacting a salt of a phosphazenium cation and an inorganic anion, represented by the following formula:
[in the above formula, m is an integer of from 1 to 3 and represents the number of phosphazenium cations, Xm− is an m-valent inorganic anion, each of a, b, c and d is a positive integer of at most 3, or 0, provided that all of them are not simultaneously 0, and R's are the same or different C1-10 hydrocarbon groups, provided that two R's on the same nitrogen atom may be bonded to each other to form a ring structure] with an alkali metal salt of an active hydrogen compound represented by M+nZn− (wherein M+n represents n alkali metal cations, n is an integer of from 1 to 8, and Zn− is a n-valent active hydrogen compound anion in the form obtained by removing n protons from an active hydrogen compound having at most 8 active hydrogen atoms on oxygen atoms or nitrogen atoms and is the same as Zn− in the above phosphazenium salt), and the above phosphazenium salt is useful as a catalyst for ring-opening polymerization of propylene oxide (e.g. Patent Document 7). However, this phosphazenium salt has had an economical problem, since its production process requires many steps, and the operation is cumbersome.
Further, it has been reported that a nitrogen-containing phosphonium salt represented by the following formula (III):[R]nP+—YmX−  (III)(in the formula, n=2 to 4, m=0, 1 or 2, n+m=4, R is —N═C(NR1R2)(NR3R4), Y is —N(R5)(R6), each of R1 to R6 which are independent of one another, is a C1-10 cyclic, aliphatic or aromatic hydrocarbon which may have a substituent, and contains at least one hetero atom or at least one chiral center, or (—CH2—CH2—O—)o—CH2CH2—Oalk (o=1 to 12), and X is an anion obtainable from an inorganic or organic acid having O, N or S bonded to active oxygen) is useful as a non-metallic catalyst for e.g. a halogen-exchange reaction or a phase-transfer catalytic reaction, production of a polyalkylene polyol polymer, polymerization of a lactam, a polyurethane or halogenated hydrocarbon polymerization reaction, or a halogen-deprotection reaction (e.g. Patent Document 8).
However, Patent Document 8 does not disclose any example for preparation of a polyalkylene polyol and teaches nothing about how to prepare a polyalkylene polyol by means of a nitrogen-containing phosphonium salt of the above formula (III) or what types of a polyalkylene polyol is thereby prepared.